Pitting corrosion aluminium

Metals which owe their good corrosion resistance to the presence of thin, passive or protective surface films may be susceptible to pitting attack when the surface film breaks down locally and does not reform. Thus stainless steels, mild steels, aluminium alloys, and nickel and copper-base alloys (as well as many other less common alloys) may all be susceptible to pitting attack under certain environmental conditions, and pitting corrosion provides an excellent example of the way in which crystal defects of various kinds can affect the integrity of surface films and hence corrosion behaviour. 

Videm, K., Pitting Corrosion of Aluminium in Contact with Stainless Steel , Proc. Conf. on Corrosion Reactor Mater., Salzburg, Austria, 1, 391 (1962) C.A., 60, 1412g Lyon, D. H., Salva, S. J. and Shaw, B. C., Etch Pits in Germanium Detection and Effects , J. Electrochem. Soc., 110, 184c (1963)... 

Bond, A. P., Bolling, G. F. and Damian, H. A., Influence of Microsegregation on Pitting Corrosion in High-purity Aluminium , J. Electrochem. Soc., 112, 178c (1965)... 

Frazer, M. J. and Langstaff, R. D., Influence of Cupric Ions on the Behaviour of Surface-active Agents Towards Aluminium , Bril. Corrosion J., 2, II (1%7) Szklarska-Smialowska, Z. and Janik-Czachor, H., Pitting Corrosion of 13Cr-Fe Alloy in Na2S04 Solutions Containing Chloride Ions , Corros. Sci., 7, 65 (1967)... 

Penn, J. H. and Murray, G. A. W., Effect of Acidic Gelatinous Materials on Pitting Corrosion of Aluminium Hollow-ware , Br. Corros. J., 2, 193 (1967)... 

Kato, M., Inoue, T. and Sato, O., New Microautoradiography Using Auger Electrons in the Study of the Structure and Pitting Corrosion of Aluminium , Proc. Symp. Nucl. Tech. Basic Metal Ind., 1972, 541 (1973)... 

Broli, A. and Holtan, H., Use of Potentiokinetic Methods for the Determination of Characteristic Potentials for Pitting Corrosion of Aluminium in a Deaerated Solution of 3< o NaCl , Corros. Sci., 13, 237 (1973)... 

Kato, M., Inoue, T., Goto, K., Ito, G. and Shimizu, Y., Effect of Dissolved Oxidising Agents and Inhibitors on Pitting Corrosion of Aluminium in Water , Aluminium, 49, 289 (1973) Richardson, J. A. and Godwin, A. W., Localised Corrosion of Stainless Steel During Food Processing , Br. Corros. J., 8, 259 (1973)... 

Sverepa, O., Pitting Corrosion of Aluminium in Water , Korose Ochrana Mater., 1 (1961) C.A., 57, 12237h... 

Freiman, L. 1. and Kolotyrkin, Ya. M., Pitting Corrosion of Aluminium in Solutions of Sodium Perchlorate and Perchloric Acid , Zashch. Melal, 2, 488 (1966) C.A., 65, 19674d Novakovskii, V. M. and Sorokina, A. N., Comparative Electrochemistry of Stress Corrosion and Pitting of Stainless Steels in Chloride Solutions , Zashch. Melal, 2, 416 (1966) C.A., 65, 18152g... 

Imoi, H., Saito, Y., Kobayashi, M. and Fujiyama, S., Pitting-corrosion-resistant Chromium Stainless Steel , Japan Kokai 7300, 221 (1973) C.A., 79, 22569a Sato, E., Tamura, T. and Okabe, T., Aluminium Anode for Cathodic Protection. 7 Pitting and Corrosion Potentials for Gallium in Sodium Chloride Solutions , Kinzoku Hyomen Gijutsu, 24, 82 (1973) C.A., T9, 12792d... 

Most simple inorganic salt solutions cause virtually no attack on aluminium-base alloys, unless they possess the qualities required for pitting corrosion, which have been considered previously, or hydrolyse in solution to give acid or alkaline reactions, as do, for example, aluminium, ferric and zinc chlorides. With salts of heavy metals —notably copper, silver, and gold —the heavy metal deposits on to the aluminium, where it subsequently causes serious bimetallic corrosion. 

Aluminium pipes Aluminium might become an important material for carrying water if its liability to pitting corrosion could be overcome. Very soft waters are difficult to accommodate when normal pipe materials are used, and it is for these that aluminium offers most promise ". The possibility of using it for domestic water pipes, however, appears at present to depend upon finding a cheap and effective inhibitor that could be added to the water, or upon the use of internally clad tube, e.g. Al-1 25 Mn alloy clad with a more anodic alloy, such as Al-lZn. Such pipes are at present mainly used for irrigation purposes. ... 

Recommended practice for examination and evaluation of pitting corrosion Test method for determining susceptibility to stress corrosion cracking of high-strength aluminium alloy products Test method for pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution Recommended practice for preparation and use of direct tension stress corrosion test specimens... 

As expected from the data in Table 7.3, galvanic corrosion is one of the major practical corrosion problems of aluminium and aluminium alloys. The reason for this is that aluminium is thermodynamically more active (less noble) than most other common structural materials, and that the passive oxide which usually protects aluminium may easily be broken down locally when the potential is raised due to contact with a more noble material. This is particularly the case when aluminium and its alloys are exposed in waters containing chlorides or other aggressive species (see also Section 7.6, Pitting Corrosion). 

Aluminium is liable to pitting corrosion in media containing chloride, but the corrosion may not necessarily be of a serious nature. However, if aluminium is... 

Cathodic protection can also be applied to prevent pitting. Regarding aluminium, strong cathodic polarization should be avoided because this can lead to a large increase of pH close to the metal surface, which can cause so-called alkaline corrosion (compare with the Pourbaix diagram for aluminium in Figure 3.11, Section 3.8). Use of sacrificial anodes of Zn or A1 alloys is therefore safer than impressed current. 

In a case of pitting corrosion on an aluminium sheet in seawater, the largest pit depth is 200 pm after 2 months. What will be the maximum depth expected after 1 year After 10 years ... 

When copper piping is used in tap water systems, one will, particularly in hot water pipes, and also in cold water pipes in periods with little or no tapping, get an increased concentration of copper ions, sometimes to a great extent. After tapping of such water into containers, pots or pans of less noble metals (e.g. aluminium), copper is deposited, and heavy pitting corrosion may occur. 

---